Plug fuse



April 22, 1958 s JONES 2,831,945

PLUG FUSE Filed Sept. 9, 1957 INVENTOR" ATTORNEYS United States Patent ice PLUG FUSE I Spurgeon R. Jones, Milan, Tenn.

Application September 9, 1957, Serial No. 682,769 7 Claims. (or. 200-115 The present invention relates in general to non-renew able plug fuses of the Edison base type, and more particularly to plug fuses arranged to afford protection against high voltage surges occurring during electrical storms as a result of lightning and against other excessive voltages or current surges. The present invention presents specific improvements on electric fuses of the type disclosed in my earlier Patent No. 2,219,705.

An object of the present invention is the provision of'a plug fuse affording protection against lightning andother high voltage and current surges which is of simple and inexpensive construction, Which is highly resistant to damage resulting from physical shock, and which is readily insertable into and withdrawable from conventional fuse cabinets and domestic fuse installations. I Another object of the present invention is the provision illustrating two preferred embodiments of the invention.

In the drawing: a I Figure l is a fragmentary section view of a conventional fuse cabinethaving a pair of plug fuses embodying the present invention installed therein, with parts broken away to illustrate one of the plug fuses in vertical transverse section; I I

Figure 2 is a fragmentary horizontal section view taken along the. line 22 of Figure 1;

Figure 3 is a fragmentary section view taken along the line 3-3 of Figure 1; s p

Figure 4 is a fragmentary section View of a fuse cabinet of a novel plug fuse arranged to afford protection against lightning and other high voltage current surges which similar to Figure 1, but illustrating a modified form of plug fuse embodying the present invention installed therein; and

Figure 5 is a fragmentary horizontal section view taken along the line 55 of Figure 4.

Referring to the drawing wherein like reference char- 2,831,945 Patented Apr. 22,, 1958 carries one or a plurality of fuse-supporting bodies 14, usually of molded insulating material. Electrical conmotions are provided beneath the front panel 13 and within the housing 11, by which the fuses are electrically interposed in the circuits they are to protect. The body 14, of insulating material carried by the front panel 13 is provided with a plurality of cylindrical wells 15 opening forwardly of the front panel 13', in which'the threaded metallic socket members'16 and spaced center terminal 17 are located for reception of the Edison base type fuse plugs.

One preferred form'of the fuse plug embodying the present invention illustrated in Figures 1,2 and 3, is indicated by the reference character 20. The fuse 'plug 20 comprises the usual ceramic or porcelain fuse body 21 having'a brass center contact 22 and a metallic screw shell 23 which are respectively designed to be in electrical communication with the center terminal 17 and threaded metallicsocket member 16. An elongated fusible link 24 is located within the bore 25 of the fuse body 2f and is connected at its opposite ends with the center contact 22 and screw'shell 23. A metal cap 26 extends over the upper end of the body 21 and comprises a disk portion 27 and an integral peripheral flange 28 which is bent about the shoulder formed at the upper portion of the fuse body 21 to retain the cap 26 in position. The central region of the disk portion 27 'of 'the'metal cap 26 is stamped or pressed to provide a downwardly projecting depression 2? which, inthe preferred embodiment, is of rounded or concave configuration' projectinga substantial distance cap26 which, in the embodiment of- Figures 1, 2and'3,

comprises a brass grounding conductor strap 32 which is in theform of a flat spring'rnemhjer bent intermediate its ends to provide'anupperleg 33 and a depending leg 34' inclined at anacute angleto each other., The end i-of the' upper, leg 33 of the, grounding strapBZfis fixed tdthe metal cap 26, preferably by soldering, at a point adjacent the periphcry' of the metal cap 26 with the ,straporiented so] that the upper leg 33' thereof extends diametrically fuse cabinet housing 11 so as to electrically ground the cap '26. 'With this construction, the plug fusev 20 will operate in theconventional manner in. ordinaryuse,v as the current fiows through the circuit established between the threaded socket member 16 and center terminal 17 0f the fuse cabinet throughthe center contact. 2 2, fusible link 1 24, and screw shell 23 of the plug fuse 20 without leakagej to ground'through the metal cap 26 and grounding strz'rpv 32 as the metal cap 26 is insulated from the fusible 24-by the mica separator 31. However, upon occurrence.

of a high voltage surge, such as may occur asa result of lightningduring electrical storms or other causes, a dielectric breakdown through the perforations of the mica sepa rator 34 occurs and the current is conducted to ground through the metal cap 26 and-grounding strap 32;

The plug fuse illustrated in Figures 4 and 5,"which isindicatedngenerally by the reference character35, comprises the same fuse body-21, center contact 22; screw shell 23, fusible link 24, metal cap -2 6 and mica separator? 31 described in connection with the embodiment of Figures 1, 2 and 3. However, it employs a different physical arrangement for grounding the metal cap 26. In the embodiment shown in Figures 4 and 5, the grounding conductor, indicated at 36, comprises a helical coil of copper or other metallic wire 37, whose convolutions are of reducing diameter progressing away from the cap to form a conico-helical coil. The lower end 38 is soldered or otherwise fixed in intimate electrical contact with the metallic cap 26 adjacent the periphery thereof with the coil arranged concentrically with the axis of the fuse body 21. The upper or free end 39 of the grounding conductor 37 is normally spaced a sufiicient distance from the metal cap 26 to contact the inner surface of the hinged cover 12 of the fuse cabinet during closing of the same and the coil 37 will be disposed in a state of compression between the cover 12 and the metal cap 26 when the fuse cabinet cover 12 is fully closed and the plug 35 is fitted in its socket.

The operation of the plug fuse 35 is similar to the above-described operation of plug fuse 20. The helical conductor coil 36 is placed under slight compression between the cover 12 of the fuse cabinet and the cap 26 of the plug fuse when the cabinet is closed and is maintained in good electrical contact with the grounded cabinet cover by the resilient bias of the spring coil 36 to provide a by-pass path to ground for current when dielectric breakdown occurs through the perforations of the mica separator 31.

While two embodiments of the invention have been shown and described, it is apparent that other modifications may be made in the invention without departing from the spirit and scope thereof, and it is desired, therefore, that only such limitations shall be placed thereon as are imposed by the prior art and are set forth in the appended claims.

I claim:

1. A plug fuse comprising a fuse body of insulating material having a central bore opening through one end thereof, spaced fuse terminals supported thereon, a fusing link within the bore of said body and connected to said terminals, a metallic cap fixed to said body closing the open end of said bore, said cap having an integral depending depression projecting into said bore into close proximity to said fusing link, a perforated insulating spacer held between and in contact with said depression and said fusing link, and a resilient metallic grounding spring fixed at one end thereof to said cap and resiliently tensioned to urge the other end thereof away from said cap into contact with a grounded surface of a fuse cabinet when the plug fuse is seated in a fuse socket of the cabinet.

2. A plug fuse comprising a generally cylindrical fuse body of insulating material having a concentric central bore therein opening through one end thereof, spaced fuse terminals supported thereon, a fusing link within said bore and connected to said terminals, a metallic cap fixed to said body having a generally disk-shaped portion extending over the end of said body having said bore opening therein and closing said bore opening, said disk portion of said cap having an integral depression formed centrally therein projecting into said bore into close proximity to said fusing link, a perforated insulating disk contacted and held between said depression and said fusing link forming a spacer through the perforations of which a dielectric breakdown may occur when the potential difference between said cap and said link exceeds a preselected value, and a resilient grounding spring of elongated metallic material having one end thereof fixed to said cap and the other end thereof resiliently projected from said cap to contact a grounded surface of a fuse cabinet when the fuse plug is mounted in a fuse socket of the cabinet.

3. A plug fuse comprising a generally cylindrical fuse body of insulating material having a concentric central bore therein opening through the upper end thereof, a

4 screw shell terminal supported on said body, a center contact body located in the lower end of said body, an elongated fusing link within said bore connected to said screw shell terminal and said center contact terminal, said fusing link being bent intermediate its ends to provide an ascending portion rising from said center contact terminal and a transverse portion extending horizontally across said bore, a metallic cap fixed to the upper end of said body in closing relation to the end of said bore opening through said body having a generally disk-shaped portion overlying said upper end of said body, said disk-shaped portion having an integral downwardly concave depression stamped therein projecting into said bore into close proximity to said transverse portion of said fusing link, a perforated mica disk contacted and held between said depression and said fusing link forming a spacer therebetween through the perforations of which a dielectric breakdown may occur when the voltage difference between said cap and said link exceeds a preselected value, and a resilient grounding spring of electrically conductive material having one end thereof fixed to said cap adjacent the periphery of the cap .and the other end thereof projecting from the cap to be urged by the resiliency of the spring into intimate electrical contact with a grounded surface of a fuse cabinet when the fuse plug is mounted in a fuse socket of the cabinet.

4. In a fuse plug, the combination recited in claim 2 wherein said grounding spring comprises an elongated flat strip spring bent intermediate its ends to provide legs lying at acute angles to each other, the end of one of said legs being fixed to said cap adjacent the periphery thereof with said one leg extending diametrically across said cap and rising slightly in inclined relation to the plane of said disk portion and the other leg depending alongside and spaced from the periphery of said cap to resiliently urge the free end of said depending portion into intimate electrical contact with the dead-front panel of a fuse cabinet when the fuse plug is mounted therein.

5. In a fuse plug, the combination recited in claim 3 wherein said grounding spring comprises an elongated flat strip spring bent intermediate its ends to provide legs lying at acute angles to each other, the end of one of said legs being fixed to said cap adjacent the periphery thereof with said one leg extending diametrically across said cap and rising slightly in inclined relation to the plane of said disk portion and the other leg depending alongside and spaced from the periphery of said cap to resiliently urge the free end of said depending portion into intimate elec trical contact with the dead-front panel of a fuse cabinet when the fuse plug is mounted therein.

6. A plug fuse comprising a generally cylindrical fuse body of insulating material having a concentric central bore therein opening through one end thereof, spaced fuse terminals supported thereon, a fusing link within said bore and connected to said terminals, a metallic cap fixed to said body having a generally disk-shaped portion extending over the end of said body having said here opening therein and closing said bore opening, said disk portion of said cap having an integral depression formed centrally therein projecting into said bore into close proximity to said fusing link, a perforated insulating disk contacted and held between said depression and said fusing link forming a spacer through the perforations of which a dielectric breakdown may occur when the potential difference between said cap and said link exceeds a preselected value, and a resilient grounding spring formed of a helical coil of metallic wire havingone end thereof fixed to said cap adjacent the periphery of the cap in concentric relation to said disk portion and the other end thereof resiliently projected by the coil away from the cap to dispose said other end in electrical contact with a grounded surface of a fuse cabinet when the fuse plug is mounted in the cabinet.

7. In a fuse plug, the combination recited in claim 3 wherein said grounding spring comprises a conicohelical coil of metallic wire having one end thereof fixed to the disk portion of said cap adjacent the periphery thereof with the convolutions of the coil arranged in concentric relation to said disk portion and ofrreducing diameter progressing away from the cap, the other end of the coil being resiliently projected by the coil away from the cap to contact the cover of a fuse cabinet when the cover is in closed position and the fuse plug is mounted in the cabinet.

References Cited in the file of this patent UNITED STATES PATENTS 

